STFC/RAL, Chilton, Didcot, Oxon
Exeter University, Exeter, Devon
Gericke LTD, Ashton-under-Lyne
This paper describes the potential of fluidised powdered material for use as a particle production target in high power particle accelerator based facilities. In such facilities a multi-MW proton beam is required to interact with a dense target material in order to produce sub-atomic particles, e.g. neutrons for a neutron source or pions for a so-called conventional neutrino beam, a neutrino factory or a muon collider. Experience indicates that thermal transport, shock wave and radiation damage will limit the efficiency and reliability of facilities utilising solid targets at around 1 MW beam power. Consequently liquid mercury has been adopted as the target technology for the latest neutron facilities SNS and J-SNS at ORNL and Tokai respectively, and is the baseline for a neutrino factory and muon collider. However mercury introduces new problems such as Cavitation Damage Erosion. This paper discusses how a fluidised powder target may combine many of the advantages of a liquid metal with those of a solid, and describes an experimental programme at RAL currently underway to implement this technology.
STFC/RAL, Chilton, Didcot, Oxon
Exeter University, Exeter, Devon
Gericke LTD, Ashton-under-Lyne
This paper proposes a technology based on fluidized powder which could be employed as a high power target (and beam dump), for example in a future Neutrino Factory or Muon Collider. A fluidized powder target is believed to bring together some advantages of both the solid and liquid phase whilst avoiding some of their drawbacks. The current Neutrino Factory and Muon Collider proposals require the use of a high Z target material withstanding beam ionisation heating of around 1 MW. The article proposes to use a dense tungsten powder jet as an alternative to the baseline open mercury jet for interaction with the proton beam inside the high field capture solenoid. The preliminary experimental results on the production and on the characteristics of a dense horizontal tungsten powder jet are presented. The morphology of the jet is analysed and presented as a function of the driving parameters (e.g. pneumatic supply pressure, boundary conditions of the jet, etc.). A test rig was developed to investigate the reliability of lean and dense phase pneumatic conveying of tungsten powder and the results of such experiments are discussed in the paper.
STFC/RAL, Chilton, Didcot, Oxon
Kyoto University, Kyoto
KEK, Ibaraki
Funding: Science and Technology Facilities Council
The T2K experiment will utilise the highest pulsed power proton beam ever built to generate an intense beam of neutrinos. This uses the conventional technique of colliding the 0.75 MW 30 GeV proton beam with a graphite target and using a magnetic horn system to collect pions of one charge and focus them into a decay volume where the neutrino beam is produced. The target is a two interaction length (900 mm long) graphite target supported directly within the bore of the first magnetic horn which generates the required field with a pulsed current of 300 kA. This paper describes the design and development of the target system required to meet the demanding requirements of the T2K facility. Challenges include radiation damage, shock waves resulting from a 100 K temperature rise in the graphite material during each beam spill, design and optimisation of the helium coolant flow, and integration with the pulsed magnetic horn. Conceptual and detailed engineering studies were required to develop a target system that could satisfy these requirements and could also be replaced remotely in the event of a target failure.
STFC/RAL, Chilton, Didcot, Oxon
KEK, Ibaraki
The target station of the T2K neutrino facility requires a beam window to separate the target chamber, containing helium at atmospheric pressure, from the secondary beam line, which is maintained at ultra high vacuum. In addition to withstanding this differential pressure, the window must survive induced stresses due to intense heating resulting from interaction with a 0.75 MW pulsed proton beam. The design consists of a hemispherical double window with forced convection helium cooling in the volume enclosed, manufactured from titanium alloy. Preliminary analysis suggested that 'shock' waves induced by the pulsed nature of the beam will form the dominant mode of stress. The finite element software ANSYS Mechanical (V10) has been used to simulate the effect of beam impingement on a variety of window thicknesses in an attempt to find the optimum geometry. Results have shown that through thickness stress waves can be amplified if successive bunches arrive in phase with the waves generated by previous bunches. Therefore, thickness has been shown to be a critical variable in determining the window’s resistance to induced thermal shock.
Sheffield University, Sheffield
University of Warwick, Coventry
STFC/RAL/ISIS, Chilton, Didcot, Oxon
STFC/RAL/ASTeC, Chilton, Didcot, Oxon
STFC/RAL, Chilton, Didcot, Oxon
Funding: Science and Technology Facilities Council (United Kingdom)
The UK programme of high power target developments for a Neutrino Factory is centred on the study of high-Z materials (tungsten, tantalum). A description of lifetime shock tests on candidate materials is given as a part of the research into a solid target solution. A fast high current pulse is applied to a thin wire of the sample material and the lifetime measured from the number of pulses before failure. These measurements are made at temperatures up to ~2000 K. The stress on the wire is calculated using the LS-DYNA code and compared to the stress expected in the real Neutrino Factory target. It has been found that tantalum is too weak at these temperatures but a tungsten wire has reached over 26 million pulses (equivalent to more than ten years of operation at the Neutrino Factory). Measurements of the surface velocity of the wire using a laser interferometry system (VISAR) are in progress, which, combined with LS-DYNA modelling, will allow the evaluation of the constitutive equations of the material. An account is given of the optimisation of secondary pion production and capture in a Neutrino Factory and of the latest solid target engineering ideas.